The technology stack of the site is pretty interesting. I wrote a little about it here:
http://leafo.net/posts/introducing_itchio.html#technology
Essentially the web app runs directly inside of nginx (but a special build of nginx from the project OpenResty[0]). The entire site is coded in MoonScript[1], which is my language that compiles to Lua.
I developed a web framework called Lapis while making this site, it doesn't have documentation yet but you can find the source here: https://github.com/leafo/lapis
I you want to see another sample Lapis webapp you can check out my MoonRocks project. The source is here: https://github.com/leafo/moonrocks-site